1. Field of the Invention
The present invention relates generally to battery chargers, more specifically to charging a battery using a wall adapter operating in a collapsed mode of operation.
2. Related Art
Portable devices, such as smart phones, mobile computers, handheld game consoles, media recorders, media players/displayers, communication devices, and personal navigation devices (PNDs) to provide some examples, are evolving into a variety of new forms with increased functionality. Although partially offset by improvements in low-power electronics, the increase in functionality carries a corresponding increase in energy consumption causing a need for more efficient batteries and battery chargers. As a result, battery chemistries, including the more popular lithium and nickel based batteries, have seen marked improvements in performance. Although batteries continue to improve, much of their potential remains dependent on the battery charger. Accordingly, the battery charger must keep pace with battery technology in order to realize the full capabilities of such batteries.
Several different types of battery chargers are commonly used, such as linear chargers or switching chargers to provide some examples. The linear charger minimizes the size and complexity of the battery charger. The linear charger simply drops an input voltage down to a battery voltage using a pass transistor such as a MOS device or a bipolar device to provide some examples. However, the linear charger dissipates a great amount of power. For example, in the case of a 1 A linear charger, a 12VDC input voltage, and battery voltage that varies between 4.2V and 2.5V, the power dissipation of the pass transistor can range from 7.8 W to 9.5 W. Commonly, this great amount of power is dissipated inside the portable device causing a tremendous amount of heat.
The switching charger has consistently low power dissipation over wide variations in input voltage. The switching charger steps the input voltage down to the battery voltage using one or more switching devices, such one or more MOS devices to provide an example. However, the switching charger tends to be large in size and greatly complex. Other disadvantages include electromagnetic interference (EMI) and other various electrical noises inside the portable device caused by the switching action of the charger.
Thus, what is needed is an apparatus and method to charge a battery that overcomes the shortcomings described above. Further aspects and advantages of this invention will become apparent from the detailed description that follows.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.